JP6717426B2 - Power converter - Google Patents

Description

The present invention relates to a power conversion device.

Conventionally, in a power conversion device including an inverter, a rectifier circuit, a smoothing circuit connected to the rectifier circuit, and a snubber circuit, the snubber circuit includes a first snubber capacitor and a first diode connected in series. A series circuit; and a second series circuit in which a second diode and a transistor are connected in series, the first series circuit is connected to an output terminal of the rectifier circuit, and one end of the second series circuit is connected to the first series circuit. Connect to the series connection point of the snubber capacitor and the first diode of the circuit, connect the other end to the series connection point of the smoothing inductor and the smoothing capacitor of the smoothing circuit, and connect the Zener diode to the base terminal of the transistor of the second series circuit. Then, what controls the electric potential of the series connection point of the second diode and the transistor of the second series circuit to a predetermined value is known (Patent Document 1).

JP, 2011-244559, A JP, 2013-116021, A

However, there is a problem that the switching element of the inverter has a large loss and is inefficient.

The problem to be solved by the present invention is to provide a power conversion device in which the switching loss of the switching element of the inverter circuit is suppressed and the efficiency is improved.

The present invention relates to an inverter circuit having a switching element, a transformer connected to the inverter circuit, a rectifier circuit that rectifies the power output from the transformer, and a snubber circuit that suppresses vibration of current flowing in the rectifier circuit. With the characteristics of the snubber circuit, the above problem is solved by increasing the suppression level of the oscillating current when the output current of the power conversion device decreases.

According to the present invention, switching loss of a switching element can be suppressed and efficiency can be improved.

FIG. 1 is a block diagram of a power conversion device according to this embodiment. FIG. 2 is a circuit diagram of the power conversion device according to this embodiment. FIG. 3 is a graph showing current or voltage characteristics in the circuit of the power conversion device shown in FIG. FIG. 4 is a graph showing current or voltage characteristics in the circuit of the power conversion device shown in FIG. FIG. 5 is a graph showing current or voltage characteristics in the circuit of the power conversion device shown in FIG. FIG. 6 is a front view of a component in which the filter inductor and the variable resistor shown in FIG. 2 are integrated. FIG. 7A is a circuit diagram of a circuit on the secondary side of the power conversion device according to the modification of the present embodiment. FIG. 7B is a circuit diagram of a circuit on the secondary side of the power conversion device according to the modification of the present embodiment. FIG. 7C is a circuit diagram of a circuit on the secondary side of the power conversion device according to the modification of the present embodiment. FIG. 7D is a circuit diagram of a circuit on the secondary side of the power conversion device according to the modification of the present embodiment. FIG. 8 is a circuit diagram of a circuit on the secondary side of a power conversion device according to another embodiment of the present invention. FIG. 9 is a block diagram of a power conversion device according to another embodiment of the present invention. FIG. 10A is a circuit diagram of the snubber circuit shown in FIG. 9. FIG. 10B is a circuit diagram of the snubber circuit of the power conversion device according to the modification of the present embodiment. FIG. 10C is a circuit diagram of a snubber circuit of a power conversion device according to a modification of this embodiment. FIG. 10D is a circuit diagram of a snubber circuit of a power conversion device according to a modification of this embodiment. FIG. 11: is a circuit diagram of the snubber circuit of the power converter device which concerns on the modification of this embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<<1st Embodiment>>
FIG. 1 is a block diagram of a power conversion device according to this embodiment. The power converter according to this embodiment is an insulating DC-DC converter. As shown in FIG. 1, the power conversion device includes an inverter circuit 10, a transformer 20, a rectifier 30, a filter circuit 40, a snubber circuit 50, and a controller 100.

The inverter circuit 10 converts the DC power input from the input terminal into AC power. The transformer 20 is a transformer for ensuring insulation, and steps up or down the voltage. The transformer 20 is connected to the output of the inverter circuit 10. The inverter circuit 10 is connected to the primary side of the transformer 20, and the rectifier 30, the filter circuit 40, and the snubber circuit 50 are connected to the secondary side of the transformer 20.

The rectifier 30 rectifies the power input from the secondary side of the transformer 20 and outputs it to the filter circuit 40. The rectifier 30 converts the AC power input from the transformer 20 into DC power. The filter circuit 40 suppresses vibration of electric power output from the rectifier 30.

The snubber circuit 50 suppresses the oscillating current generated in the circuit of the power converter. The snubber circuit 50 is connected to at least one of the rectifier 30 and the filter circuit 40. For example, when the current rectified by the rectifier 30 suddenly changes in a short time, a surge voltage is generated at the input end of the filter circuit 40. A snubber circuit 50 is connected to suppress the surge voltage.

The controller 100 controls ON/OFF of a switching element included in the inverter circuit 10.

An example of a circuit diagram of the power converter according to this embodiment will be described with reference to FIG. FIG. 2 is a circuit diagram of the power conversion device according to this embodiment.

The inverter circuit 10 includes switching elements S1 to S4, freewheeling diodes D1 to D4, capacitors 11 to 14, and a smoothing capacitor 15. The switching elements S1 to S4 are MOSFETs. The switching elements S1 to S4 may be transistors such as IGBTs. The switching elements S1 to S4 are connected so as to form a full bridge circuit. The switching element S1 and the switching element S2 are connected in series, and the switching element S3 and the switching element S4 are connected in series. The connection point between the switching element S1 and the switching element S2 is connected to one end of the primary side coil 21 of the transformer 20, and the connection point between the switching element S3 and the switching element S4 is the other side of the primary side coil 21 of the transformer 20. Connected to the end. Freewheeling diodes D1 to D4 and capacitors 11 to 14 are connected to the switching elements S1 to S4, respectively. The return diodes D1 to D4 are connected in parallel to the switching elements S1 to S4 so that the conduction directions of the return diodes D1 to Dd are opposite to the current conduction directions (forward direction) of the switching elements S1 to S4. ing. The free wheeling diodes D1 to D4 may be parasitic diodes of the switching elements S1 to S4, and the capacitors 11 to 14 may be parasitic capacitances of the switching elements S1 to S4. A smoothing capacitor 15 is connected between the input terminals of the inverter circuit 10.

The transformer 20 has a primary coil 21 and secondary coils 22a and 22b. The primary coil 21 is connected to the output of the inverter circuit 10. The secondary side of the transformer 20 is of a center tap type, and wiring is connected to a connection point between the secondary coil 22a and the secondary coil 22b. The primary side coil 21 and the secondary side coils 22a and 22b are insulated from each other. The transformer 20 boosts or lowers the voltage according to the winding ratio (Np/Ns) of the primary coil 21 and the secondary coils 22a and 22b.

The rectifier 30 has a diode D31 and a diode D32. The anode terminal of the diode D31 is connected to the secondary coil 22a, and the cathode terminal of the diode D31 is connected to the filter inductor 41. The anode terminal of the diode D32 is connected to the secondary coil 22b, and the cathode terminal of the diode D32 is connected to the connection point that connects the cathode terminal of the diode D31 and the filter inductor 41.

The filter circuit 40 is an LC filter and has a filter inductor 41 and a filter capacitor 42. The filter inductor 41 is connected to the positive power supply line. The filter capacitor 42 is connected to the output side of the filter circuit 40, and is connected between the positive power supply line and the negative power supply line. The negative power supply line is connected to a connection point between the secondary coil 22a and the secondary coil 22b. The rectifier 30 and the filter circuit 40 correspond to the secondary side rectifier circuit.

The snubber circuit 50 includes a capacitor 51 and a variable resistor 52. The capacitor 51 and the variable resistor 52 are connected in series, and the series circuit of the capacitor 51 and the variable resistor 52 is connected in parallel to the filter inductor 41.

Next, the circuit operation of the power conversion device according to this embodiment will be described.

The two half bridges output a square wave voltage by the controller 100 controlling ON/OFF of the switching elements S1 to S4. The controller 100 controls the switching elements S1 to S4 so that the duty ratio of the square wave voltage is 50%. Due to the phase shift of the two square wave voltages, an alternating current flows through the primary coil 21 of the transformer 20. An AC voltage is applied to the transformer 20, and power is transmitted to the secondary side of the transformer 20.

In this embodiment, since the switching operation of the switching elements S1 to S4 is soft switching, the circuit configuration is such that partial resonance occurs in the circuit on the primary side of the power conversion device. Partial resonance is generated in the LC circuit of the drain-source capacitance of the switching elements S1 to S4 and the leakage inductance (L _rec ) of the transformer. Since the partial resonance occurs during the dead time period of the switching elements S1 to S4, the switching elements S1 to S4 are turned on by zero vector switching (ZVS), so that the switching operations of the switching elements S1 to S4 are performed. It becomes soft switching.

Further, when the switching elements S1 to S4 are turned off, the drain-source capacitance (hereinafter also referred to as the DS capacitance) of the switching elements S1 to S4 is charged, so that the increase in the drain-source voltage is delayed. As a result, the overlap period of the voltage and the current at the time of turn-off can be shortened, and soft switching can be realized.

In order to realize soft switching at turn-on, the discharge of the DS capacitances of the switching elements S1 to S4 must be completed during the dead time period. When the discharge of the DS capacitance ends during the dead period, even if the switching elements S1 to S4 are turned on, the discharge current of the DS capacitance does not flow to the switching elements S1 to S4 that are turned on. The overlapping period of voltage and current is shortened, and soft switching can be realized. On the other hand, during the dead time period, when the switching elements S1 to S4 are turned on in a state where the discharge of the DS capacitance is not finished, the discharge current of the DS capacitance flows to the turned-on switching element, so that the hard switching is performed. And the switching loss becomes large.

In order to discharge the DS capacity during the dead time period, a current sufficient to promote the discharge must flow in the primary side of the transformer 20. That is, when the primary side current of the transformer 20 is low during the dead time period, the discharge current of the DS capacitance becomes small, and therefore the discharge of the DS capacitance does not end during the dead time period. Further, when the direction of the primary side current of the transformer 20 changes during the dead time period, the forward current flows through the freewheeling diodes D1 to D4 connected to the switching elements S1 to S4 in the off state, The DS capacitances of the switching elements S1 to S4 about to turn on are charged. Therefore, the turn-on operation of the switching elements S1 to S4 becomes hard switching, and the output voltage of the inverter circuit 10 becomes unstable.

Next, the relationship between the current flowing through the transformer 20 and the output current of the power conversion device will be described. 3, the input voltage of the primary winding 21 _(V L, V _R) characteristic of the characteristics of the primary current of the transformer 20 _{(I TR),} the current flowing through the diode D31, D32 of the rectifier 30 (I _D1, characteristics of _{I D2),} is a graph showing current _{(I L)} characteristic of the filter inductor 41, and the voltage of the filter inductor 41 _{(V rec)} characteristics. The input voltage (V _L ) corresponds to the output voltage of one of the two half bridges of the inverter circuit 10, and the input voltage (V _R ) corresponds to the output voltage of the other.

As shown in FIG. 3, when the output voltage (V _L ) of the half bridge of the inverter circuit 10 rises at time t ₁ , the primary side current (I _TR ) of the transformer 20 increases with a positive slope. At this time, the primary-side current _{(I TR)} is the relationship between the input voltage _{(V in)} and leakage inductance _{(L s),} represented by the following formula (1).

While the primary-side current (I _TR ) changes according to the slope of the equation (1), the current (I _D1 ) flowing through the diode D31 of the rectifier 30 increases and the current (I _D2 ) flowing through the diode D32 increases. Decrease. That is, the current on the secondary side of the rectifier 30 is circulating.

Then, at time _{t 2, the} transformer secondary side of the current _{(I D1)} is a current value obtained by multiplying turns ratio (Np / Ns) to the transformer primary current _{(I TR)} match. In time _{t 2, the} inclination of the primary current _{(I TR)} becomes gentler than (inclination represented by the formula (1)) slope between the time _{t 1} to _{t 2,} the following formula (2) expressed.

Since the current (I _L ) flowing through the filter inductor 41 changes abruptly as the primary current (I _TR ) changes at the time t ₂ , the surge voltage (V _rec ) easily occurs at the output of the rectifier 30. In FIG. 3, the point at which the current (I _L ) of the filter inductor 41 sharply changes is represented by the circle surrounded by the dotted line, and the surge voltage is likely to occur at the dotted line portion.

Primary current _{(I TR),} the time _{t 2} later, gradually increases with a constant slope, a time _{t 3} after, slowly decreases with a constant gradient. Time _{t 3} is a timing the half-bridge output voltage of the inverter circuit 10 _{(V R)} rises. Then, at the timing (time t ₄ ) when the output voltage (V _L ) of the half bridge of the inverter circuit 10 falls, the primary current (I _TR ) greatly decreases.

The output current (I _L ) of the filter inductor 41 gradually increases with a constant slope after time t ₂ , and gradually decreases with a constant slope after time t ₃ . Then, the output current (I _L ) gradually increases again at time t ₅ . Transformer secondary side of the current _{(I D2)} are timing value of current multiplied by the turns ratio of the (Np / Ns) to the transformer primary current _{(I TR)} coincide is time _{t 5.}

That is, between time t ₂ and time t ₄ , electric power is transmitted from the input to the output of the power conversion device, and the primary side current (I _TR ) and the output current (I _L ) change gently. Then, from time t ₂ to time t ₄ , the absolute value of the output current (I _L ) is a value obtained by multiplying the absolute value of the primary side current (I _TR ) by the winding ratio (Np/Ns). Become. Further, since the output current (I _out ) of the power converter is a value obtained by averaging the current (I _L ) of the filter inductor 41, the average of the output current (I _out ) matches the average of the current (I _L ). To do.

Then, the output current of the power converter (I _out) is the characteristics when the output current (I _out) is lower than when shown in FIG. 3 will be described with reference to FIG. Figure 4, similar to the voltage-current characteristic shown in FIG. 3, in order from the top in FIG. 4, the input voltage characteristics _{(V L, V R),} 1 primary current characteristics _{(I TR),} the current characteristic of the diode D31, D32 (I _D1 , I _D2 ), the current characteristic (I _L ) of the filter inductor 41, and the voltage characteristic (V _rec ) of the filter inductor 41 are shown. FIG. 4 shows characteristics when the output current of the power converter is lower than the output current (I _out ) shown in FIG.

The timing of the rising and falling of the half-bridge output voltage of the inverter circuit 10 _{(V L,} V _R) is the same as FIG. When the output current (I _out ) is low, the current (I _L ) of the filter inductor 41 becomes low. The primary side current (I _TR ) has a linear relationship with the current (I _L ) of the filter inductor 41. Therefore, the primary side current (I _TR ) also becomes low.

The dead time period (t _d ) is from time t ₁ to time t ₂ . That is, when the output current (I _out ) is low, the primary side current (I _TR ) becomes low in the dead time period (t _d ). Then, when the primary side current ( _ITR ) decreases to such an extent that the DS capacitances of the switching elements S1 to S4 cannot be discharged during the dead time period (t _d ), the switching operation of the switching elements S1 to S4 is hard. It will be switching.

Further, at the end point timing (t ₂ , t _4, etc.) of the dead time period (t _d ), a surge voltage is likely to occur. When the surge voltage is generated in the circuit on the secondary side of the power converter, an oscillating current is generated by charging and discharging the junction capacitance of the diodes D31 and D32 included in the rectifier 30. The oscillating current on the secondary side resonates via the transformer 20 due to the leakage-in inductor (L _s ) on the primary side of the transformer 20. That is, the oscillating current on the secondary side causes the current on the primary side to oscillate.

The influence of the oscillating current on the primary side during the dead time period will be described with reference to FIG. FIG. 5 shows the characteristics of the input voltage (V _L ) of the primary winding 21, the switching operation characteristics of the switching elements S1 and S2 (configuration of the drive signals of the switching elements S1 and S2), and the primary of the transformer 20. The characteristics of the side currents ( _{ITR_a} , _{ITR_b} ) are shown. The high level of the switching operation characteristic indicates the on state, and the low level indicates the off state. The primary side current ( _{ITR_a} ) indicates a current when the vibration suppression level of the snubber circuit 50 is high, and the primary side current ( _{ITR_b} ) indicates a current when the vibration suppression level of the snubber circuit 50 is low.

At time _{t 1,} when the switching element S2 is turned off, the primary current of the transformer _{20 (I} TR_а, _{I TR_b)} is flowing in the negative direction. When a negative current is flowing on the primary side of the transformer 20, the DS capacity is discharged. When the vibration suppression level of the snubber circuit 50 is high, the current vibration on the secondary side is suppressed, so that the current on the primary side does not oscillate and the primary side does not oscillate from time t ₁ to time t _2. The current direction of the current ( _{ITR_a} ) remains negative and does not change. During the dead time, a negative current continues to flow in the primary side of the transformer 20, so that the DS capacity is discharged during the dead time. Then, at the end of the dead time period, the turn-on operation of the switching element S1 becomes soft switching.

On the other hand, when the vibration suppression level of the snubber circuit 50 is low, the current vibration on the secondary side is not suppressed, so that the current vibration on the secondary side also occurs on the primary side. The primary side current _{(I TR_а)} is low, the current in the primary is vibrated, the period from time _{t 1} to time _{t 2, the} direction of current in the primary current _{(I TR_b)} is negative Changes in the positive direction. If the primary side current ( _{ITR_b} ) becomes positive before the upper switching element S1 is turned on, a forward current flows through the freewheeling diode D2 of the lower switching element S2. When the upper switching element S1 is turned on (time t ₂ ), a voltage corresponding to the input voltage (V _in ) should be input to the primary winding 21 of the transformer 20. However, since the free wheeling diode D2 is conducting, the voltage applied to the primary winding 21 becomes the reference voltage (potential on the negative side of the input voltage), and the output voltage of the inverter circuit 10 becomes unstable. .. Further, during the dead time period, the direction of the primary-side current ( _{ITR_b} ) changes from negative to positive, so that the DS capacitance of the upper switching element S1 is charged. Therefore, the switching operation of the switching element S1 becomes hard switching, and switching loss increases.

That is, in order to suppress the oscillating current during the dead time period, the vibration suppression level of the snubber circuit 50 should be high. However, increasing the vibration level of the snubber circuit 50 increases the loss of the snubber circuit. In particular, when the output current (I _out ) is high, the primary side current (I _TR ) during the dead time period is sufficiently high to discharge the DS capacitance of the switching elements S1 to S4, and the primary side current (I _TR ). The direction of ( _ITR ) is rarely affected by the generation of the oscillating current on the secondary side. That is, the characteristics of the vibration suppression level of the snubber circuit 50 (hereinafter, also referred to as vibration suppression characteristics) may be such that the vibration suppression level becomes higher as the output current (I _out ) becomes lower. As a result, when the output current (I _out ) is high, the vibration suppression level becomes low, and the loss of the snubber circuit 50 can be suppressed. Further, when the output current (I _out ) is low, the vibration suppression level becomes high, and the soft switching operation of the switching elements S1 to S4 can be realized while suppressing the secondary side vibration current.

In the present embodiment, the snubber circuit 50 has the structure described below because the characteristics of the snubber circuit 50 are the vibration suppression characteristics described above. FIG. 6 is a front view of a component in which the filter inductor 41 and the variable resistor 52 are integrated.

The filter inductor 41 has a magnetic core 411 and an inductor coil 412. The magnetic core 411 is a magnetic body that covers the inductor coil 412 and the variable resistor 52. The inductor coil 412 is a pair of coils. The current flowing through the inductor coil 412 is the current of the filter inductor 41 and corresponds to the output current (I _out ) of the power conversion device.

The variable resistor 52 is a magnetoresistive element such as an MR element or a GMR element. The variable resistor 52 is provided in the gap of the magnetic core 411. When the output current of the rectifier circuit 31 flows through the inductor coil 412, the inductor coil 412 generates a magnetic field, and the magnetic core 411 forms a magnetic circuit. The variable resistor 52 is arranged in the magnetic circuit. The magnetic field generated by the inductor coil 412 is proportional to the current of the filter inductor 41. Further, the variable resistor 52 has a positive characteristic with respect to the magnetic field, and the resistance value of the variable resistor 52 increases as the magnetic field strength increases. The snubber circuit 50 is connected in parallel with the filter inductor 41, and the higher the current of the filter inductor 41, the higher the resistance value of the snubber circuit 50. The higher the resistance value of the snubber circuit 50, the lower the suppression level of the oscillating current by the snubber circuit 50 becomes.

Since the resistance value of the snubber circuit 50 decreases as the current of the filter inductor 41 decreases, the suppression level of the snubber circuit 50 increases. On the other hand, as the current of the filter inductor 41 becomes higher, the resistance value of the snubber circuit 50 becomes higher and the suppression level of the oscillating current by the snubber circuit 50 becomes lower. That is, the magnetic field strength generated in the filter inductor becomes a parameter having a correlation with the output current, and the suppression level of the oscillating current by the snubber circuit 50 changes according to the parameter. Although the surge voltage increases due to the decrease in the vibration suppression level of the snubber circuit 50, the peak value of the surge voltage is suppressed below the reference value. The reference value is an upper limit value of the voltage determined by the rated voltage or the like of the circuit elements included in the power converter, and is set in advance.

When the current on the primary side is low, the output current (I _out ) of the power converter and the current of the filter inductor 41 are low, and the suppression level of vibration by the snubber circuit 50 is high. Therefore, since the oscillating current on the secondary side is suppressed, the direction of the primary side current does not change during the dead time period and is maintained in the negative direction. Accordingly, when the output current (I _out ) of the power conversion device is low, soft switching of the switching elements S1 to S4 can be realized. The current range in which soft switching is possible expands with respect to the magnitude of the output current (I _out ) of the power conversion device.

Further, when the primary side current is high, the output current (I _out ) of the power converter and the current of the filter inductor 41 are high, and the loss of the snubber circuit 50 is reduced.

As described above, the power conversion device according to this embodiment includes the inverter circuit 10, the transformer 20, the rectifier 30, and the snubber circuit 50. The snubber circuit 50 has the characteristic that the suppression level of the oscillating current by the snubber circuit 50 becomes higher when the output current of the power conversion device becomes lower. Thereby, the switching loss of the switching element can be suppressed and the efficiency can be improved.

Further, in the present embodiment, the switching elements S1 to S4 operate by soft switching using LC resonance. Thereby, switching loss is suppressed and efficiency can be improved.

Further, in the present embodiment, the suppression level of the oscillating current by the snubber circuit 50 changes according to the parameter having the correlation with the output current of the power conversion device. As a result, the suppression level of the oscillating current changes passively, so that the vibration suppressing characteristic can be realized with a simple configuration.

Further, in the present embodiment, the variable resistor 52 is composed of a magnetic resistance element, and the magnetic resistance element is arranged in the magnetic circuit generated by the filter inductor 41. As a result, the resistance of the snubber circuit 50 changes passively, so that the vibration suppressing characteristic can be realized with a simple configuration.

Further, in the present embodiment, the filter inductor 41 is arranged in the gap of the magnetic core 411. As a result, the vibration suppressing characteristic can be realized with a simple configuration.

In addition, in the present embodiment, the diodes D31 and D32 are configured by devices that do not operate in the reverse recovery operation. Accordingly, when the output current of the power conversion device is high, the surge voltage is suppressed, so that the suppression level of the oscillating current by the snubber circuit can be further lowered. As a result, the snubber circuit loss can be reduced.

As a modified example of the present embodiment, since the snubber circuit 50 has a vibration suppressing characteristic, the variable resistor 52 included in the snubber circuit 50 may be a resistor having a positive temperature characteristic. The resistance having a positive temperature characteristic is, for example, a PTC resistance. When the current flows through the snubber circuit 50, the temperature of the variable resistor 52 rises due to self-heating. Since the resistance of the variable resistor 52 increases as the temperature of the variable resistor 52 rises, the effect of suppressing the oscillating current by the snubber circuit 50 decreases, and the loss of the snubber circuit 50 is suppressed. As a result, the vibration suppressing characteristic can be realized with a simple configuration.

Further, when the variable resistor 52 is a resistor having a positive temperature characteristic, the variable resistor 52 may be arranged near the transformer 20 or the rectifier 30. When a current flows through the power converter, the elements included in the transformer 20 or the rectifier 30 generate heat. By arranging the variable resistor 52 in the vicinity of the transformer 20 or the rectifier 30, the variable resistor 52 is in a state capable of heat exchange with the element serving as the heat source. As a result, the vibration suppressing characteristic can be realized with a simple configuration.

Further, as a modified example of the present embodiment, since the snubber circuit 50 has a vibration suppressing characteristic, the capacitor 51 included in the snubber circuit 50 may be a capacitor having a negative temperature characteristic. When the current flows through the snubber circuit 50 and the temperature of the capacitor 51 rises, the capacitance of the capacitor 51 decreases, so the effect of suppressing the oscillating current by the snubber circuit 50 is reduced, and the loss of the snubber circuit 50 is suppressed. As a result, the snubber circuit 50 can be configured to have a vibration suppressing characteristic.

When the capacitor 51 is a capacitor having a negative temperature characteristic, the capacitor 51 may be arranged near the transformer 20 or the rectifier 30. When a current flows through the power converter, the elements included in the transformer 20 or the rectifier 30 generate heat. By disposing the capacitor 51 close to the transformer 20 or the rectifier 30, the capacitor 51 is in a state capable of heat exchange with the element serving as the heat source. As a result, the vibration suppressing characteristic can be realized with a simple configuration.

The capacitor 51 or the variable resistor 52 according to the modification may be arranged so as to be adjacent to the temperature-dependent filter inductor 41, the magnetic core 411, and the diodes D31 and D32. As a result, the capacitance of the capacitor 51 or the resistance value of the variable resistor 52 easily changes with temperature.

Note that the snubber circuit 50 does not need to be connected in parallel to the filter inductor 41 as shown in FIG. 2, but may be connected between the filter inductor 41 and the reference potential of the output voltage as shown in FIG. 7A or 7B. Good. The reference potential of the output voltage corresponds to the negative potential of the output voltage of the power converter.

7A and 7B are circuit diagrams on the secondary side of a power conversion device according to a modification. The configurations of the rectifier 30 and the filter circuit 40 are the same as the above configurations. As shown in FIG. 7A, the snubber circuit 50 has a capacitor 51, a diode 53, and a resistor 54. The capacitor 51 is connected to the cathode of the diode 53, and the series circuit of the capacitor 51 and the diode 53 is connected between a pair of power supply lines of the filter circuit 40. One end of the resistor 54 is connected to a connection point that connects the capacitor 51 and the diode 53, and the other end of the resistor 54 is connected to a connection point that connects the filter inductor 41 and the filter capacitor 42.

As shown in FIG. 7B, the snubber circuit 50 has a capacitor 51 and a resistor 54. The series circuit of the capacitor 51 and the resistor 54 is connected between a pair of power supply lines of the filter circuit 40.

The rectifier 30 may be a full bridge rectifier circuit as shown in FIGS. 7C and 7D. 7C and 7D are circuit diagrams on the secondary side of the power conversion device according to the modification. The configuration of the filter circuit 40 is similar to the above. As shown in FIG. 7C, the secondary coil of the transformer 20 is composed of a single coil. The rectifier 30 is composed of a full bridge circuit of diodes D31 to D34. The snubber circuit 50 is connected in parallel to the diodes D31 to D34, respectively. The snubber circuit 50 has a capacitor 51 and a resistor 54, and the capacitor 51 and the resistor 54 are connected in series.

As shown in FIG. 7D, the coil on the secondary side of the transformer 20 is composed of a single coil. The rectifier 30 is composed of a full bridge circuit of diodes D31 to D34. The snubber circuit 50 has the same configuration as the snubber circuit 50 shown in FIG. 7A. The connection form between the filter circuit 40 and the snubber circuit 50 is the same as the connection form shown in FIG. 7A.

The rectifying element included in the rectifier 30 is not limited to the diodes D31 to D34, and may have a circuit configuration in which a diode and a transistor such as a MOSFET are connected in parallel. When transistors are used, the rectifier circuit may be a synchronous rectifier circuit in which the on and off operations of each transistor are synchronized.

The diodes D31 and D32 included in the rectifier 30 may be devices without reverse recovery operation, such as Schottky barrier diodes. A surge voltage is generated by charging and discharging the junction capacitance of the diodes D31 and D32, and an oscillating current is generated by the surge voltage in the secondary side circuit of the power conversion device. When the diodes D31 and D32 are devices that do not involve reverse recovery operation, the oscillating current does not depend on the value of the current flowing through the diodes D31 and D32, but depends on the voltage applied to the diodes D31 and D32. Therefore, when the current on the secondary side increases, the surge voltage can be suppressed. As a result, the vibration suppression level in the high current region is suppressed, the loss of the snubber circuit 50 is reduced, and the efficiency is improved.

<<Second Embodiment>>
A power converter according to another embodiment of the present invention will be described. In the present embodiment, the suppression level of the oscillating current by the snubber circuit 50 is set to a plurality of levels according to the magnitude of the output current of the power conversion device. The power converter according to the present embodiment is different from the first embodiment in the configuration of the snubber circuit 50, and for the other configurations, the description of the first embodiment is appropriately incorporated.

FIG. 8 is a circuit diagram of the secondary side of the power conversion device. The snubber circuit 50 includes a capacitor 51, resistors 54a and 54b, and a transistor 55. The capacitor 51, the transistor 55, and the resistor 54a are connected in series, and the series circuit of the capacitor 51, the transistor 55, and the resistor 54a is connected in parallel to the filter inductor 41. The control terminal (base terminal or gate terminal) of the transistor 55 is connected to the positive power supply line of the filter circuit 40 via the resistor 54b. The current input from the rectifier 30 to the filter circuit 40 is branched at the connection point between the filter inductor 41 and the resistor 54b. Therefore, the control current (base current or gate current) flowing through the control terminal of the transistor 55 is a current that is inversely proportional to the output current (I _out ) of the power conversion device. The collector and emitter of the transistor function as a variable resistor. That is, when the output current (I _out ) of the power converter decreases, the control current of the transistor 55 increases and the resistance of the transistor 55 decreases. Therefore, when the resistance value of the snubber circuit 50 decreases, the suppression level of the oscillating current by the snubber circuit 50 increases. Thus, the snubber circuit 50 can be configured such that the snubber circuit 50 has a vibration suppressing characteristic.

Further, by configuring the transistor 55 so that the resistance between the collector-emitter or the drain-source of the transistor 55 changes in multiple steps with respect to the control current, the suppression level of the oscillating current by the snubber circuit 50 can be set to a plurality of levels. Therefore, the plurality of suppression levels change according to the magnitude of the output current of the power converter. As a result, the loss of the snubber circuit 50 can be reduced while expanding the range of the output current (I _out ) that can be operated by soft switching.

As described above, in the present embodiment, the suppression level of the oscillating current by the snubber circuit 50 is set to a plurality of levels according to the magnitude of the output current (I _out ). As a result, the suppression level can be changed in multiple stages while having a correlation with the output current (I _out ), so that the efficiency is improved.

Further, in the present regulation, the snubber circuit 50 has the transistor 55, and the relation between the current at the control terminal of the transistor and the output current (I _out ) of the power conversion device is inversely proportional. As a result, the vibration suppressing characteristic can be realized with a simple configuration.

Note that the transistor 55 may be a switching element that can be energized in both directions. Further, the transistor 55 is a normally-on switching element, and even if the circuit on the secondary side of the power conversion device is configured such that the negative bias voltage of the gate of the transistor 55 increases as the output current (I _out ) increases. Good. As a result, the characteristics of the snubber circuit 50 can be made to be the vibration suppression characteristics, so that the efficiency can be improved while suppressing the switching loss of the switching element.

<<Third Embodiment>>
A power converter according to another embodiment of the present invention will be described. In the present embodiment, the snubber circuit 50 has a switch, and the vibration suppression characteristic is realized by controlling the on/off of the switch. The power converter according to the present embodiment is different from the first embodiment in the configuration of the snubber circuit 50 and the control of the snubber circuit 50, and other configurations are the same as those in the first embodiment or the second embodiment. The description is incorporated as appropriate.

FIG. 9 is a block diagram of the power conversion device according to this embodiment. The power conversion device includes a current sensor 200 in addition to the inverter circuit 10 and the like. The current sensor 200 is connected to the output side of the filter circuit 40 and detects the output current (I _out ) of the power conversion device. The current sensor 200 outputs the detected current to the controller 100. For the current sensor 200, a sensor such as a Hall current sensor is used. The controller 100 switches ON/OFF of a switch included in the snubber circuit 50 according to the detected voltage acquired from the current sensor 200. The current sensor 20 may be connected to the input side of the filter circuit 40.

The snubber circuit 50 has at least a switch 56. The switch 56 is a semiconductor switch. The switch 56 is not limited to a semiconductor switch and may be a mechanical contact switch. A specific circuit configuration of the snubber circuit 50 is shown in FIG. 10A. FIG. 10A is a circuit diagram of the snubber circuit 50. The snubber circuit 50 includes a capacitor 51, resistors 54a and 54b, and a switch 56. The capacitor 51 and the resistor 54a are connected in series. The resistor 54b and the switch 56 are connected in series. The series circuit of the resistor 54b and the switch 56 is connected in parallel to the resistor 54a.

When the switch 56 is in the ON state, the resistance value of the snubber circuit 50 is the combined resistance value of the resistors 54a and 54b. When the switch 56 is off, the resistance value of the snubber circuit 50 is the resistance value of the resistor 54a. The resistance value of the snubber circuit 50 changes depending on whether the switch 56 is turned on or off, so that the suppression level of the oscillating current by the snubber circuit 50 changes. That is, the switch 56 is a switch that switches the suppression level of the snubber circuit 50.

The controller 100 outputs a drive voltage or drive current for controlling the on/off of the switch 56 to the snubber circuit 50. The driving power source is built in the snubber circuit 50. The controller 100 stores the current threshold value in the memory. The current threshold value is a threshold value for determining whether the switchon is turned on or off, and is set in advance. The controller 100 compares the current threshold value with the current detected by the current sensor 200, and switches the switch 56 on and off according to the comparison result.

The controller 100 may be divided into one for controlling the inverter circuit 10 and one for controlling the snubber circuit 50. Further, the control signal for switching the switch 56 on and off may be insulated. Thereby, the threshold value for varying the vibration suppression level of the snubber circuit can be adjusted.

When the resistance value of the snubber circuit 50 is low when the switch 56 is on and high when the switch 56 is off, the controller 100 controls the switch 56 as follows. When the detected current (I _out ) of the current sensor is equal to or higher than the current threshold value, the controller 100 turns off the switch 56 to increase the resistance value of the snubber circuit 50. The suppression level of the snubber circuit 50 becomes a low level, and the loss of the snubber circuit 50 is suppressed. On the other hand, when the detected current (I _out ) of the current sensor is less than the current threshold value, the controller 100 turns on the switch 56 to lower the resistance value of the snubber circuit 50. The suppression level of the snubber circuit 50 becomes high, and the vibration suppression effect of the snubber circuit 50 is enhanced, so that the soft switching operation can be realized.

As described above, in the present embodiment, the snubber circuit 50 has the switch 56 that switches the suppression level, and the controller 100 switches the switch 56 on and off according to the magnitude of the current detected by the current sensor 200. This makes it possible to obtain the vibration suppression characteristic while controlling the vibration suppression level in multiple stages according to the magnitude of the output current (I _out ).

The snubber circuit 50 is not limited to the circuit configuration shown in FIG. 10A and may have another circuit configuration. Examples of other circuit configurations are shown in FIGS. 10B to 10D are circuit diagrams of the snubber circuit 50 according to the modification.

As shown in FIG. 10B, the snubber circuit 50 includes capacitors 51a and 51b, a resistor 54, and a switch 56. The capacitor 51a and the resistor 54 are connected in series, and the capacitor 51b and the switch 56 are connected in series. The series circuit of the capacitor 51b and the switch 56 is connected in parallel to the capacitor 51b. By changing the capacitance of the snubber circuit 50 by turning on and off the switch 56, the suppression level of the snubber circuit 50 can be switched in multiple stages.

As shown in FIG. 10C, the snubber circuit 50 includes capacitors 51a and 51b, a resistor 54, and a switch 56. The capacitors 51a and 51b and the resistor 54 are connected in series. The switch 56 is connected in parallel with the capacitor 51b. By changing the capacitance of the snubber circuit 50 by turning on and off the switch 56, the suppression level of the snubber circuit 50 can be switched in multiple stages.

As shown in FIG. 10D, the snubber circuit 50 includes a capacitor 51, resistors 54a and 54b, and a switch 56. The capacitor 51, the resistor 54a, and the resistor 54b are connected in series. The switch 56 is connected in parallel with the resistor 54a. By changing the resistance value of the snubber circuit 50 by turning the switch 56 on and off, the suppression level of the snubber circuit 50 can be switched in multiple stages.

The snubber circuit 50 may be a circuit in which the circuits shown in FIGS. 10A to 10D are combined, and the conduction circuit and the non-conduction circuit may be switched according to the magnitude of the output current (I _out ).

In addition, as a modification of the present embodiment, the snubber circuit 50 may include a plurality of protection circuits having different suppression levels. FIG. 11 is a circuit diagram of the snubber circuit 50 according to the modification. As shown in FIG. 11, the snubber circuit 50 includes switches 56a and 56b and protection circuits 57a to 57c. The protection circuits 57a to 57c are series circuits in which capacitors 51a to 51c and resistors 54a to 54c are connected in series. The capacitors 51a to 51c are capacitors having different electrostatic capacitances, and the resistors 54a to 54c are resistors having different resistance values. That is, the protection circuits 57a to 57c are snubber circuits that are independent of each other and have different vibration suppression levels. The switch 56a is connected between the protection circuit 57a and the protection circuit 57b, and the switch 56b is connected between the protection circuit 57b and the protection circuit 57c.

The controller 100 switches between conduction and non-conduction of the protection circuits 57a to 57c by switching the switches 56 and 56b on and off according to the magnitude of the detected current detected by the current sensor 200. As a result, the suppression level of the snubber circuit 50 can be switched in multiple stages.

As a modification of the present embodiment, the snubber circuit 50 may be connected to the rectifier 30 or the filter circuit 40 via a switch. Then, the controller 100 turns off the switch and disconnects the snubber circuit 50 according to the magnitude of the output current (I _out ). As a result, when the suppression of vibration by the snubber circuit 50 is not necessary, the snubber circuit 50 can be separated, so that the efficiency can be improved.

10... Inverter circuits 11-14... Capacitor 15... Smoothing capacitor 20... Transformer 21... Primary side coil 22, 22a, 22b... Secondary side coil 30... Rectifier circuit 40... Filter circuit 50... Snubber circuit 100... Controller 200... Current sensors D1 to D4... Return diodes D31 to 34... Diodes S1 to S4... Switching elements

Claims (16)

In the power converter,
An inverter circuit having a switching element,
A transformer connected to the inverter circuit;
A rectifier circuit that rectifies the power output from the transformer,
A snubber circuit for suppressing the oscillation of the current flowing through the rectifier circuit,
The snubber circuit has a characteristic that the suppression level of the oscillating current becomes higher when the output current of the power converter becomes lower. The power converter according to claim 1, wherein the suppression level is set to a plurality of levels according to the magnitude of the output current. The power conversion device according to claim 1, wherein the switching element operates by soft switching using LC resonance. The power conversion device according to claim 1, wherein the suppression level changes according to a parameter having a correlation with the output current. The rectifier circuit has an inductor,
The snubber circuit has a magnetoresistive element,
The power conversion device according to claim 1, wherein the magnetoresistive element is arranged in a magnetic circuit generated by the inductor. The inductor has a magnetic core,
The power conversion device according to claim 5, wherein the magnetoresistive element is arranged in a gap of the magnetic core. The power conversion device according to claim 1, wherein the snubber circuit includes a resistance element having a positive temperature characteristic. The power conversion device according to claim 7, wherein the resistance element is arranged in proximity to at least one of the rectifier circuit and the transformer. The power conversion device according to claim 1, wherein the snubber circuit includes a capacitance element having a negative temperature characteristic. The power conversion device according to claim 9, wherein the capacitance element is arranged in proximity to at least one of the rectifier circuit and the transformer. The snubber circuit has a transistor,
The power converter according to any one of claims 1 to 4, wherein the relationship between the current flowing through the control terminal of the transistor and the output current is inversely proportional. A sensor for detecting the output current,
A controller for controlling the snubber circuit,
The snubber circuit has a switch for switching the suppression level,
The power conversion device according to any one of claims 1 to 4, wherein the controller switches the switch on and off according to a detection current detected by the sensor. A sensor for detecting the output current,
A controller for controlling the snubber circuit,
The snubber circuit has a plurality of protection circuits having different suppression levels,
The power conversion device according to claim 1, wherein the controller switches between conduction and non-conduction of the protection circuit according to a detection current detected by the sensor. The power converter according to claim 12 or 13, wherein the snubber circuit includes at least one circuit element of a switch, a resistor, and a capacitor. A controller for controlling the snubber circuit,
The power conversion device according to claim 1, wherein the controller switches between conduction and non-conduction of the snubber circuit according to the value of the output current. The power conversion device according to claim 1, wherein the rectifier circuit includes a Schottky barrier diode.

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